Cell Lines for Studies in Heart

I want to carry out studies for heart. currently, i am using H9C2 cells (a
rat cell line) and primary rat cardiomyocytes to do my experiments. however,
my supervisor suggests me to use the P19 cell line (a mouse cell line) which
can have the beating activity and this is a big advantage over H9C2 cells.
But using P19 cells will shift my model from rats to mice and that's my
problem.
I would like to ask if there are any rat cell lines which also have the
beating activity (As far as i ve searched in ATCC, there are no such cell
lines). also, which cell line do u prefer, H9C2 or P19? Thanks
Samantha